1. Field of the Invention
This invention relates to a radiation image recording and read-out apparatus for recording a radiation image of an object, and reading out the radiation image to obtain electric image signals. This invention particularly relates to a radiation image recording and read-out apparatus wherein a radiation image is recorded on a stimulable phosphor sheet capable of storing the radiation energy, and subdivision image recording on the stimulable phosphor sheet is carried out easily.
2. Description of the Prior Art
When certain kinds of phosphors are exposed to a radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, cathode rays or ultraviolet rays, they store a part of the energy of the radiation. Then, when the phosphor which has been exposed to the radiation is exposed to stimulating rays such as visible light, light is emitted by the phosphor in proportion to the stored energy of the radiation. A phosphor exhibiting such properties is referred to as a stimulable phosphor.
As disclosed in U.S. Pat. Nos. 4,258,264, 4,276,473, 4,315,318 and 4,387,428 and Japanese Unexamined Patent Publication No. 56(1981)-11395, it has been proposed to use a stimulable phosphor in a radiation image recording and reproducing system. Specifically, a sheet provided with a layer of the stimulable phosphor (hereinafter referred to as a stimulable phosphor sheet) is first exposed to a radiation passing through an object such as the human body to have a radiation image of the object stored thereon, and is then scanned with stimulating rays which cause it to emit light in proportion to the stored radiation energy. The light emitted by the stimulable phosphor sheet upon stimulation thereof is photoelectrically detected and converted to electric image signals, which are processed as desired to reproduce a visible image having an improved image quality, particularly a high diagnostic efficiency and accuracy. The finally obtained visible image may be reproduced in the form of a hard copy or may be displayed on a cathode ray tube (CRT). In this radiation image recording and reproducing system, the stimulable phosphor sheet is used to temporarily store the radiation image in order to reproduce the final visible image therefrom on a final recording medium. For economical reasons, therefore, it is desirable that the stimulable phosphor sheet be used repeatedly.
In order to reuse stimulable phosphor sheets as mentioned above, the radiation energy remaining on the stimulable phosphor sheet after it is scanned with stimulating rays to read out the radiation image stored thereon should be erased by exposing the stimulable phosphor sheet to light or heat as described in, for example, U.S. Pat. No. 4,400,619 or Japanese Unexamined Patent Publication No. 56(1981)-12599. The stimulable phosphor sheet should then be used again for radiation image recording.
From the aforesaid viewpoint, the applicant proposed in Japanese Unexamined Patent Publication No. 59(1984)-192240 which corresponds to U.S. application Ser. No. 037,119 (Con. Appln. of U.S. Ser. No. 600,689), now U.S. Pat. No. 4,851,679 a radiation image recording and read-out apparatus comprising:
i) a circulation and conveyance means for conveying at least one stimulable phosphor sheet for recording a radiation image thereon along a predetermined circulation path, PA0 ii) an image recording section disposed on the circulation path for recording a radiation image of an object on the stimulable phosphor sheet by exposing the stimulable phosphor sheet to a radiation passing through the object, PA0 iii) an image read-out section disposed on the circulation path and provided with a stimulating ray source for emitting stimulating rays for scanning the stimulable phosphor sheet carrying the radiation image stored thereon at the image recording section, and a photoelectric read-out means for detecting light emitted by the stimulable phosphor sheet scanned with the stimulating rays to obtain electric image signals, and PA0 iv) an erasing section disposed on the circulation path for, prior to the next image recording on the stimulable phosphor sheet for which the image read-out has been carried out at the image read-out section, having the stimulable phosphor sheet release the radiation energy remaining on the stimulable phosphor sheet, PA0 i) a recording and read-out unit provided with: PA0 ii) a shutter provided on a radiation incidence side with respect to said stimulable phosphor sheet held at said image recording position, having a size covering at least a part of said stimulable phosphor sheet, and moveable between a masking position at which said shutter prevents impingement of the radiation upon a part of said stimulable phosphor sheet and a retracted position at which said shutter allows impingement of the radiation upon approximately the overall area of the single image recording region of said stimulable phosphor sheet, PA0 iii) a shutter operation means operated from the exterior for moving said shutter between said masking position and said retracted position, PA0 iv) a unit movement means for moving said recording and read-out unit so that said stimulable phosphor sheet at said image recording position is moved approximately in the same plane, and PA0 v) a subdivision image recording operation means for, upon receiving a subdivision image recording instruction, operating said shutter operation means to move said shutter to said masking position, and operating said unit movement means to move said recording and read-out unit so that the uncovered portion of said stimulable phosphor sheet at said image recording position that is not covered by said shutter changes sequentially. PA0 i) a recording and read-out unit provided with: PA0 ii) a shutter provided on a radiation incidence side with respect to said stimulable phosphor sheet held at said image recording position, having a size covering at least a part of said stimulable phosphor sheet, and moveable between a masking position at which said shutter prevents impingement of the radiation upon a part of said stimulable phosphor sheet and a retracted position at which said shutter allows impingement of the radiation upon approximately the overall area of the single image recording region of said stimulable phosphor sheet, PA0 iii) a shutter operation means operated from the exterior for moving said shutter between said masking position and said retracted position, PA0 iv) a sheet movement means for subdivision image recording, said sheet movement means moving said stimulable phosphor sheet at said image recording position approximately in the same plane, and PA0 v) a subdivision image recording operation means for, upon receiving a subdivision image recording instruction, operating said shutter operation means to move said shutter to said masking position, and operating said sheet movement means for subdivision image recording to move said stimulable phosphor sheet so that the uncovered portion of said stimulable phosphor sheet at said image recording position that is not covered by said shutter changes sequentially.
whereby the stimulable phosphor sheet is circulated through the image recording section, the image read-out section and the erasing section, and reused for radiation image recording. With the radiation image recording and read-out apparatus having such a configuration, the radiation image recording and read-out can be carried out sequentially and efficiently.
On the other hand, in the medical diagnosis, it is often desired to record two images of the same object under different conditions and/or by use of different image recording methods and to compare the two images, for example, as in the case where a front image and a side image of the human body are to be recorded or in the case where a set of images such as images prior to and after the injection of contrast media are to be recorded. In this case, it is desired that the two images be recorded on halves of a single stimulable phosphor sheet. With the aforesaid radiation image recording and read-out apparatus, even though the two images are recorded respectively on different stimulable phosphor sheets, the two images can be reproduced side by side on a single recording medium or on a single display device at the time of image reproduction. However, in order to efficiently utilize the stimulable phosphor sheet (to reduce the running cost) and to shorten the processing time, the two images should preferably be recorded respectively on halves of a single stimulable phosphor sheet in the course of image recording.
Also, besides the case of the recording of a set of images, the image recording region on a single stimulable phosphor sheet should preferably be divided into two or more subdivisions, and the image recording should preferably be carried out at the respective subdivisions, thereby to reduce the running cost.
Accordingly, the applicant proposed in Japanese Unexamined Patent Publication No. 61(1986)-98340 which corresponds to U.S. application Ser. No. 789,259, now U.S. Pat. No. 4,820,922 a radiation image recording and read-out apparatus wherein the stimulable phosphor sheet is circulated and conveyed and the subdivision image recording is carried out easily. The proposed radiation image recording and read-out apparatus comprises the aforesaid circulation and conveyance means for the stimulable phosphor sheet, the image recording section, the image read-out section, the erasing section, a shutter provided between the stimulable phosphor sheet at the image recording section and a radiation source for partially preventing the radiation from impinging upon the stimulable phosphor sheet in the course of the subdivision image recording, a shutter operation means for controlling the movement of the shutter, and a subdivision image recording operation means for operating the shutter operation means in accordance with a subdivision image recording instruction to move the shutter to a masking position and controlling the circulation and conveyance means to feed the stimulable phosphor sheet step-wise at the image recording section.
The aforesaid shutter is moveable between the masking position at which the shutter prevents the impingement of the radiation upon at least a part of the stimulable phosphor sheet and a retracted position at which the shutter allows impingement of the radiation upon approximately the overall area of the stimulable phosphor sheet. The shutter has a size covering at least one half of the stimulable phosphor sheet, and is formed of a material such as lead having a high radiation absorptivity.
With the proposed radiation image recording and read-out apparatus, the subdivision image recording can be carried out easily.
However, the radiation image recording and readout apparatus having the aforesaid configuration wherein the stimulable phosphor sheet is circulated and conveyed along the circulation path and sequentially sent to the image recording section, the image read-out section and the erasing section, has the drawback that the apparatus becomes large.